Devices (which will also be referred to as “wearable devices”) that are worn and used by human bodies or other living bodies have been gaining widespread use with smaller and lighter electronic parts. Many of the wearable devices are directly attached to living bodies or directly come into contact with the skin or body parts of the living bodies when used.
For example, headphones that have already been used widely are small audio reproduction devices that are attached to the area near the earholes of humans when used, and convert electrical signals output from reproduction devices and receivers into audio signals through speakers positioned near the ears or eardrums. Audio reproduction devices of this type each emit sounds to allow only the listener wearing the audio reproduction device to listen to the sounds, so that the audio reproduction devices are used in a variety of environments.
Many of the currently popular headphones are shaped to be plugged into the ears of listeners. For example, inner ear headphones belong to an “earplug type,” and the tips of the sound conduits including earpieces (or ear tips) made from a flexible material are plugged into ear canal entrances of listeners. Earpieces including shade-shaped films made from silicone rubber are in the mainstream (see, for example, Patent Literature 1). Moreover, there appear earpieces each of which includes a foamed material in the space between the shade-shaped outer sheath and the sound wave path (see, for example, Patent Literature 2), and earpieces the whole of which is formed from a foamed material, and which uses the cushioning characteristics to close ear canals.
Urethane-based foamed materials such as polyurethane are in the mainstream at the time when the present application is filed. However, urethane-based foamed materials easily hydrolyze. Accordingly, urethane-based foamed materials are insufficient for wearable devices from the perspective of durability. For example, in a case where an earpiece the whole exterior of which is formed from polyurethane is used directly in contact with the skin (such as the inner wall of the ear canal) of a living body, the surface of the earpiece hydrolyzes and deteriorates because of sweat. The comfortability is gradually lost. Further, in a case where an earpiece the whole of which is made from polyurethane is manufactured through in-mold foaming, the outer periphery of the earpiece that directly comes into contact with an earhole (inner wall of the ear canal) becomes hard or sticky because of the coating, resulting in the decreased comfortability. Further, in a case where an earpiece the whole of which is made from polyurethane is processed through slicing or cutting, all the shapes that the earpiece can have is a simple one such as a solid of revolution, resulting in the decreased comfortability. Alternatively, processing an earpiece having a complicated shape through slicing or cutting increases the cost.